Many important responses of steroids, such as meiosis resumption, sperm activation, GnRH releasing, antiapoptosis, and sexual behavior changes, occur rapidly within seconds or minutes via a nongenomic mechanism. This pathway does not require the presence of a nucleus or gene transcription. The nongenomic signaling pathways of steroids are poorly understood, mainly due to the controversies surrounding the identity of the responsible receptors. The rapid action of the steroid hormone progestin is a model for these nongenomic steroid actions. Recently, several candidate proteins, membrane progestin receptors (mPRs), nuclear progestin receptor, and progestin receptor membrane components have been suggested to be the nongenomic progestin receptor in vertebrates, including humans. However, further studies are required to determine their physiological functions, their signaling, and potential interactions. Currently, it is not clear which one is the primary receptor or, alternatively, whether a set of complementary proteins are needed for nongenomic signaling. We will use a loss-of-functional approach to study the roles and nongenomic progestin signaling of these purported nongenomic progestin receptors in zebrafish knockout models. We will generate knockouts using TALENs (transcriptional activator-like effector nucleases), a simple, cost- effective and highly efficient knockout method. Thereafter, we will examine effects of knockouts in animal fertility, maturation competency, and changes in oocyte maturation, sperm activation and nongenomic progestin signaling in the germ cells. This proposed study will be the first to generate and characterize knockout models for purported nongenomic progestin receptors. Our long- term goals are to determine the functions and signaling of nongenomic steroid receptors in vertebrates and to develop specific antagonists and agonists for fertility control or treatments of infertility. Our short-term goal is to generate genetically modified models to solve the most hotly contested issues, i.e. if mPRs are the receptors responsible for the nongenomic progestin signaling, and whether a single or multiple classes of receptors is/are involved in the nongenomic progestin signaling.